Conventional image compression systems suffer from a number of problems. They are unable to exploit visual masking and other properties of the Human Visual System (HVS) which vary spatially with image content. One reason is that the quantization parameters used by these algorithms are, typically, relatively constant over the extent of the image. As a result, images are unable to be compressed efficiently. Also, to achieve a target bit-rate or visual quality using this method, the image must be compressed multiple times.